Eddy current (EC) inspection is commonly used to detect flaws in material properties such as residual stress, density, and degrees of heat treatment, as well as detect any cracks, pings, dings, or raised material on surfaces of manufactured components such as gas turbine engine components. EC inspection is required for most aircraft engine components on which abnormal indications are detected to ensure the engine's integrity until the next maintenance schedule. During this type of inspection, electromagnetic induction is used to induce eddy currents in the component being inspected. An array of coils inside an eddy current probe generates alternating magnetic fields, which induce the eddy currents when the probe is moved near the component. When flaws are present in the component, the flow of eddy currents is altered, thereby indicating the flaw to the inspector. The altered eddy currents produce changes in a secondary magnetic field, which are detected by the array of coils inside the eddy current probe. The array generates an electrical signal in response to the altered secondary magnetic field, where the amplitude of the electrical signal is generally proportionate to the size of the flaw.
In order to effectively inspect the surface and maintain the integrity of the EC signal, smaller sized coils are used to enable maneuvering around the surface of the component. A small coil typically used is around 0.02 inches, and is effective at detecting any imperfections in the surface of the component, however these small coils are also extremely sensitive to the inspection equipment. Further, the coil has to travel with a constant pressure in relation to the specimen. To enable easier inspection of the components with the probes, the probes are often designed smaller, so they can fit into the smaller areas of the component surface. Changes in the probe shape prevent the probe from being positioned a uniform distance from the inspected component. Further, due to variations in size and shape of the component being inspected, gaps sometimes occur between the probe and the component surface, which also prevents the probe from being positioned at a uniform distance from the component. For years it has been a challenge to place a moving probe in close proximity with the component while maintaining a normal angle and normal pressure at positions sufficient for accurate readings. Even with the current, more sophisticated methods and probes available on market, the procedure to align the probe for inspection can be very time consuming, where the small features of the components are particularly difficult to align with the probe.
One current method for EC inspections uses an alignment template for each individual inspection feature. The EC probe is aligned with the alignment template, which results in an accurate inspection, assuming the template is correctly aligned with the component. This alignment template method requires the construction of a precise template, repeating the steps of realigning the template to the component, aligning the probe to template, detaching the template, and finally checking the probe alignment with the component. This current method adds the unnecessary high cost of producing the templates as well as high labor costs and delays timely delivery.
Another method for EC inspection, described in “Eddy current inspection Method” U.S. Pat. No. 6,907,358, improves the alignment process and increases productivity. However, this method is a manual process that is slow and cumbersome. Because the alignment of the EC touch probe for EC inspection is visually or audibly checked manually by a technician to ensure that no gap existed between the probe and the component surface, the component was required to be re-inspected due to the changes in the various technician's perception. Also, this method is dangerous, as to effectively hear or see the probe touching the component surface, the technician often has to dangerously place his or her head near the moving parts, or bend and twist into uncomfortable positions to ensure that the alignment is correct. Further, some areas that require inspection are small and located between engine blades or in unreachable cavities. Since these areas are difficult and often impossible to reach, the manual alignment method cannot effectively inspect those areas. Lastly, since the manual alignment method is time consuming and often consumes a significant amount of a technician's time. Because so much of a technician's time is dominated by the alignment method, the method is costly as well.
Therefore what is needed is a method and system that is directed to an accurate and efficient EC inspection process that can reduce errors, alleviate safety concerns, and lower production costs.